The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head can include a magnetic write pole and a magnetic return pole, the write pole having a much smaller cross section at the ABS than the return pole. The magnetic write pole and return pole are magnetically connected with one another at a region removed from the ABS. An electrically conductive write coil induces a magnetic flux through the write coil. This results in a magnetic write field being emitted toward the adjacent magnetic medium, the write field being substantially perpendicular to the surface of the medium (although it can be canted somewhat, such as by a trailing shield located near the write pole). The magnetic write field locally magnetizes the medium and then travels through the medium and returns to the write head at the location of the return pole where it is sufficiently spread out and weak that it does not erase previously recorded bits of data.
A magnetoresistive sensor such as a GMR or TMR sensor can be employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, or barrier layer, sandwiched between first and second ferromagnetic layers, referred to as a pinned layer and a free layer. First and second leads are connected to the sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but is free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos Θ, where Θ is the angle between the magnetizations of the pinned and free layers. In a read mode, the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
Magnetic recording hard disks drives with patterned magnetic recording media have been proposed to increase data density. In a patterned medium, the magnetic recording layer on the disk is patterned into small isolated data islands arranged in concentric data tracks. To produce the required magnetic isolation of the patterned data islands, the magnetic moment of the spaces between the islands must be destroyed or substantially reduced to render these spaces essentially nonmagnetic. In one type of patterned media, the data islands are elevated, spaced-apart pillars that extend above the disk substrate surface to define troughs or trenches on the substrate surface between the pillars. The magnetic recording layer material is then deposited over the entire surface of the substrate to cover both the ends of the pillars and the trenches. The trenches are recessed from the tops of the pillars so they are far enough from the read/write head to not adversely affect reading or writing.
A magnetic disk drive also include servo electronics, designed to keep the read and write heads centered over a desired data track. If the read and write heads wander off of the desired data track, the servo electronics correct move the slider to back to the correct location over the desired track of data. However, because the components such as the actuator, suspension and slider have a certain amount of mass, it takes time to return the slider to the correct portion over the desired data track. During the time that it takes to correct the location of the slider over the data tracks, the write head can inadvertently write to an adjacent track, resulting in loss of data. Therefore, there remains a need for a system for preventing loss of data when the slider becomes offset from the desired data track. This system would preferably be virtually instantaneous in order to prevent the loss of data during implementation of the system.